Governing the output of electrical amplifiers



7 Sept 1933 F. K. VREELAND 1,926,129

GOVERNING THE OUTPUT OF ELECTRICAL AMPLIFIERS Filed Aug. 1928 3Sheets-Sheet l A D AFI m l gn im INPUT P pp? [4J2 1 I W I z 42:8 4 n n ii (IA INVENTOR wu yw 0J2 W Sept. 12, 1933. VREELAND 1,926,129

' GOVERNING THE OUTPUT OF ELECTRICAL AMPLIFIERS Filed Aug. 3, 1928 3Sheets-Sheet 2 7 x gr INVENTOR s'sgfifce 12 figg o K, VREELAND 1,926,129

' GOVERNING THE OUTPUT OF ELECTRICAL AMPLIFIERS Filed Aug. 3, 1928 3Sheets-Sheet 5 INPUT Patented Sept 12, 1933 GOG THE OI'JTPWE FELECTRECAL AMPBS Frederick R. Vreeland, Monte, N. 31.

Application August 3,, 1928. Serial No. 297,33?

13 Claims.

The invention herein described has for its principal object thecontrolling of the output, or

specifically, the volume of sound delivered by an r amplifier, andparticularly the automatic governing of such output or sound volume.

The invention is applicable to amplifiers of various types but it isparticularly useful in con nection with radio phone receivers. When soused it permits signals of widely varying strength to be received andamplified, and it governs au-= tomatically the output or the volume ofthe sound delivered by the apparatus.- In the preferred arrangeinent itlimits such output or the volume of such sound to a predeterminedmaximum which is substantially constant and independent of the inputstrength of the signals applied to the receiver. It also provides foradjustment of the maximum so that the limit may be set at any desiredoutput within the capacity of the apparatus.

The automatic governing feature is particularly useful when applied toradio receivers for broad cast receptionwhich include selecting meansfor receiving at will any one of a number of differ ent transmissions.In such receivers, as ordinarily constructed; if the volume control isset for a signal of a given strength and the frequency selector is thenadjusted to a stronger or wealier signal, the reception usually is notsatisfactory until the volume control is readjusted by hand. By means ofthe present invention it is possible to tune in or select any one of anumber of dilierent signals of widely varying strength and in each casethe output level will be the same or have the same limiting value,whatever the input signal strength may be. A simple adjustment permitsthe setting of the output limit at any desired point. In certain caseswhere it is not always desirable to have the output level constant. theinvention may be used to limit the out= put to any desired maximum whilepermitting manual control of the output within this limit, in which casethe automatic governing feature will prevent excessive output in thecasebf strong signals or careless adjustment of the manual volumecontrol.

These results are, accomplished by deriving from the amplifier agoverning I E. F. (the commonly accepted abbreviationior electronic tiveforce) depending upon the output strength or sound volume and using thisgoverning E. M. F. to control the gain of the amplifier. In thepreferred embodiment of the invention the governing is accomplishedbyderiving from the amplifler an alternating-E. M. F. depending upon, and

preferably proportional to, theoutput strength or sound volume,rectifying such portion of this output E. M. F. as exceeds a givenvalue, producing by the rectification a floating charge in a governorelement and using the E. M. F. of the floating charge to govern the gainof the amplifier. Preferably the alternating E. M. F. derived from theamplifier, which may be called the output E. M. F. since it representsor depends upon the output strength, is derived from the demodulatedoutput of a radio frequency amplifier and detector or demodulator andhas a value depending on the amplified modulation and in the fullestembodiment of the invention is superimposed on a direct and preferablyadjustable control E. M. F., and the resulting algebraic sum of thealternating and direct E. M. Ffs is applied to a rectifier. The negativeof the control E. M. F. is connected to the anode of the rectifier andthe positive to the cathode, so that ordinarily no current flows throughthe rectifier from the direct current source. i /hen the peak value ofthe alternating or output E. M. exceeds the value of the direct orcontrol E. M. F... at the moments when the peaks are positive thealgebraic sum of the direct and alternating E. M. F.s will be positiveand a current will flow through the rectifier. This rectified current isused to charge a fiotation condenser which constitutes the governorele-- ment, whose charge builds up until it reaches a point where its E.M. F. is equal to the excess of the positive peaks over the fixednegative control E. M. F. When the floating charge reaches this pointrectification ceases. The amount of the floating charge depends upon thepeak value of the alternating or output E. M. F. which in turn dependsupon. or is proportional to the output or sound volume. The use of aflotation condenser as the governor element has the et feet of steadyingthe governing action by keeping the governing E. M. F. and hence thegain oi the amplifier substantially constant over a consider able time,thus permitting transitory changes in the output level and giving a truerendition oi speech or musia'while maintaining a definite lim itinglevel.

The floating charge in the governor element is used to control the gainof the amplifying sys= tern which supplies the output in such mannerthat the gain is reduced as the floating charge in creases. This may beaccomplished by regulating the supply of space current to the amplifieror a part thereof. The result may be accomplished in various ways. Forexample, in one arrangement the governing E. M. F. of the floatingcharge is used to control the effective impedance of a ballast orregulator tube inserted in the plate supply of one or more of theamplifier tubes, so cutting down the current and voltage supplied to theamplifier and thus controlling its gain. In another arrangement thegoverning E. M. F. is used to supply a floating bias for the amplifiertubes, this bias being increased with increasing signal strength to suchan extent that the gain of the amplifier is diminished. In a thirdarrangement the governing E. M. F. is used.

to control the output of a rectifier which supplies the anode current ofone or more of the amplifier tubes, in such manner that the rectifiedvoltage or current is cut down as the signal strength increases and thegain of the amplifier is correspondingly reduced- These arrangementswhich are chosen for illustration are typical of the various possibleembodiments of the invention which will be readily understood.

It is desirable to combine the various novel features of the inventionin a single apparatus, including the feature of deriving the governingE. M. F. from the demodulated output, the use of a floating chargeobtained by rectification to perform the governing function, the use ofa regulator tube to control the gain of the amplifier, and the devicesemployed to secure quick response and slow recovery in the operation ofthe governor, but certain advantages of the invention may be obtained byemploying some of these features without the others.

In each case, when a strong signal or input 'is applied to the systemthe amplified output, if

it exceeds the predetermined limiting level, causes a rectified currentto flow which builds up a floating charge in the governor element orcondenser, thus reducing the gain of the amplifier and tending to reducethe output E. M. F. and so limit the accumulation of the floatingcharge. After a brief interval a condition of equilibrium is reached inwhich the floating charge of the governor condenser becomes constant,and this floating charge has an E. M. F. which is added to the controlE. M. F. and raises the limit at which rectification can occur. This E.M. F. also operates to reduce the gain of the amplifying system to apoint'which produces the desired output or sound volume, and this outputor sound volume is represented by an alternating or output E. M. F.insumcient to produce further rectification except .as this may berequired to replenish the charge in the flotation condenser or governorelement.

It will be understood that the stronger the in put signals, the largerthe floating charge in the governor element will become and hence thesmaller the gain of the amplifier. When the parts of the system aresuitably proportioned, as hereinafter explained, the governing actionmay be made very sensitive, so that signals of widely varying inputstrength will he reduced to a substantially constant output level.

The invention will be described with reference to the accompanyingdrawings in which it is illustrated and in which:

Figure 1 represents a typical embodiment of the invention in schematicform.

Figure 2 is a diagram illustrating the relation of the various E. M. F.sin the system.

Figure 3 represents different application of the invention in which thegoverning E. M. F. operates on the grids of the amplifier tubes.

Figure 4 shows another application of the invention in which thegoverning E. M. F. operates to control the output of the anode supplyrectifier.

Figure 1 shows schematically a self contained governor G which iscapable of use with amplifiers of widely varying form, and illustratesthe application of the governor in governing the output of an amplifierA. The mode of employing the governor to regulate the gain of theamplifier here shown is to control the current or E. M. F. supplied tothe anodes of the amplifier by a ballast or regulator element B in theanode supply circuit, whose effective impedance is varied by thegoverning E. M. F. The regulator element here shown is a three-electrodetube 13, of the heater type whose control electrode is operated by thegoverning E. M. F. This type of tube is desirable since it permitsvariation in the D. C.

' potential of the cathode.

In the drawings the amplifier is shown as comprising a radio frequencyportion including two stages, RF-l and RF-Z, a detector D and an audiofrequency portion including a first stage AF-1 and a power stage P. Thegovernor is shown as operating to control the gain of the radiofrequency portion, RF-1 and RE -2, this arrangement being desirablesince it leaves the detector and audio frequency amplifier operatingalways at normal load so that they may be designed to meet the mostfavorable conditions of distortionless operation. Governing the radiofrequency amplifier is desirable also because a very wide range ofsignal strengths can be thus controlled without distortion. The range ofpermissible signal strengths that can be eifectively handled may beincreased to any desired degree by increasing the number of radiofrequency stages controlled by the governor.

It will be understood that the apparatus thus shown is merely typicaland illustrative. the invention not being limited to any particulararrangement of the amplifier proper.

Associated with the amplifier and preferably in its output circuit, is asuitable means for taking off an alternating E. M. F. depending on theoutput level, which is here shown as a transformer T1 whose primary coilis shunted across the output circuit and whose secondary coil suppliesthe output E. M. F. which operates the governing system. The transformerT1 may have a step-up or stepdown ratio, depending on the value of theoutput E. M. F. required to give the governor system the desiredsensitivity, as explained later.

The governing system includes a rectifier R, preferably of the wellknown type including an anode and a thermionic cathode.

The secondary of the transformer T1 is connected across the terminals ofthe rectifier R through a flotation condenser or governor element C anda source of direct or control E. M. F., E0. This control E. M. F. ispreferably adjustable, for example by means of a battery andpotentiometer as shown. The negative terminal of the control E. M. F.,E0, is connected to the anode of the rectifier and the positive terminalto the cathode as shown. Tie alternating or output E. M. F. of thetransformer T1 is thus superimposed on the direct or control E. M. E,E0, and the resulting E. M. F. is applied to the rectifier through theflotation condenser or governor elementC.

The terminals of the condenser C are connected through suitable chokecoils L, L to the cathode and the control electrode respectively of theregulator or ballast tube B, as shown, in such manher that any floatingcharge accumulating in the 15p condenser C-will be communicated to "thecon-- trol electrode of the regulator tube. It is usually desirable toemploy the choke coils L, L to exclude any alternating component orsudden changes in the governing E. M. F. from the reg-' ulator andamplifier and permit the passage of the relatively steady floating orgoverning E. M. F. only. It is also desirable to employ a secondcondenser C further to steady the governing E. M. F.

It shares with the condenser C the functions of the flotation orgovernor element. The choke coils L, L, "and either of the condensers C,C, as a separate element, may be omitted, though the use of bothcondensers and the choke coils as shown gives a steadier governing E. M.F.

The operation of the apparatus is as follows:

Any signal impulses applied to the radio frequency amplifying systemRF-i and RF2 through the input terminals I are amplified and thenapplied to the detector or demodulator D, where they are demodulated orconverted into audio frequency currents. These audio frequency currentsare amplified by the audio frequency amplifier AF whose gain and powercapacity are so chosen as to deliver the desired output to or producethe desired sound volume in a loud speaker or other translating devicelocated in the output circuit.

The transformer T1 derives from the amplifier an alternating output E.M. F. proportional to the output or" the system and depending on theamplified modulation and impresses it on the rectifier tube R in serieswith the direct or control E. M. l t, E0. The positive excess of theoutput E. M. F, EA, over the negative control E. M. F., E0, is rectifiedin the rectifier tube R and builds up a floating charge in the governorelement C, C whose E. M. 1". depends upon the positive excess of EA overE0.

The relations of the different E. M. F35 is shown in the theoreticaldiagram Fig. 2. Here EA represents the alternating or output E. M. F.depending upon and preferably proportional to the output, and E0represents the direct or control E. M. F. on which it is superimposed.If the peak value E1 of the alternating E. M. F, EA is less than E0 thenno positive E. M. F. will be impressed on the rectifier tube It and norectification will occur. Ii however the peak value of EA exceeds E0, asshown, then the excess of the positive peak E1 over the steady negativeE. M. i i, E0, will be represented by the difference ED, which impressesa positive E. M. F. on the anode of the rectifier tube. A rectifiedcurrent will then flow through the tube and a charge will accumulate inthe condensers constituting the governor element 0, C and thisrectification and accumula-= tion will continue until the floating E. M.F., which builds up in the condensers equals the difierential E. M. F.,En. Rectification will then cease, and becomes a substantially steadygoverning E. M. F.

The governing E. M. F. is communicated to the regulator tube B throughthe choke coils L, L, builds up a floating negative potential on thegrid and thus increases the effective impedance of the tube, cuttingdown the flow of space current through the regulator tube and theamplifier, thus reducing the gain of the amplifier and limiting thestrength of the output.

It will be seen that any excess in the output or sound volume beyond thepoint which makes the peak value of the output E. M. R, EA, equal to thecontrol E. M. F., Eu, results in building up a charge in the governorelement, whose E. M. F.

sesame cuts down the gain of the amplifier to a degree depending on theamount of excess of EA over E0.

The actual values of EA and E0 are chosen according to the value of thegoverning E. M. F. required to give the desired range oi regulation ofthe amplifier gain, and according to the desired sensitivity of thegoverning function.

The level of the output limit is readily altered at will by suitablychoosing or adjusting the control E. M. E, E0, as by the potentiometershown. If E0 is made small the flotation begins and the gain is reducedwhen the output is relatively small. Ii E0 is made larger the limit ofthe output level is raised. Thus by adjusting the control E. M. E, E0,the output limit may be set at will at any desired point. When sodetermined the output cannot exceed the limit level except by the smallamount determined by the sensitivity of the governor, and this amountmay be made as small as desired, as will now be explained.

The degree of sensitivity of the governing function may be determined atwill by choosing the relation'oi the output E. M. F, EA, to theparticular means employed to regulate the gain of the amplifier. If thesystem is so designed that the output E. M. R, EA, is normally largecompared to the governing E. M. F., En, required to regulate the gain ofthe amplifier, then a slight proportional increaseoi the output E. M. F.above that which over-flows the level oi the control E. M. i k, E0, willproduce a large actual increase in the governing E. M. F, and this willbe suificient to reduce the gain of the amplifier to a point whichproduces the desired output. The governing effect then becomes verysensitive and only a slight increase in the output level above thedesired limit will be permitted. Any desired sensitivity, or permissibleincrease of the output above the normal, may be obtained by suitablychoosing the parts, particularly the relation of the output is. M. F.and the control E. M. F. to the required governing E. M. F.

If desired, the condensers C-and C and associated parts may be made withhigh insulation, so that a floating charge, once accumulated in thegovernor element, will remain for a long time. The system will thenreproduce variations in the tone values or relative strength of theinput in their true relative proportions, while preventing the outputfrom exceeding the desired limiting level. This is desirableparticularly in the case of reproduction of music, to preserve theproper dynamic proportions of the composition. It is desirable howeverto provide means for restoring the sensitivity of the apparatus whenchanging to a weaker signal or input. This restoration may beaccomplished automatically by shunting a high resistance leal: R1 acrossthe governor ele-- ment as shown. When the input strength decreases thefloating charge will be slowly dissipated through this leak and thesensitivity of the system is thus restored. It the resistance R1 and thecapacity C-l-C' are made large enough the leak circuit will have a hightime constant, so

.that the system is not sensitive to temporary variatz'ons in the inputstrength, which are truly reproduced in the output, but when the inputstrength falls permanently below a given level the sensitivity isrestored after a length of time that may be determined at will by choiceof the values of 0+0 and R1. The quick response and slow recovery thussecured are desirable characteristics of the invention espec ally whenthe governing function is dependent on the amplified modulation, as inthe arrangement shown. This results in maintaining the output level at avalue that is independent of the degree 01' modulation of the carrierwave, but which reproduces, nevertheless, all the shadings or variationsin dynamic of music or speech.

In some cases it is desirable to employ a key K, with or without theleak resistance R1, so that the gain of the system, once determined bythe floating E. M. F. resulting from a given signal strength, willremain constant and not subject to further fluctuation until thesensitivity of the system is restored by closing the key K anddischarging the condensers C+C. I

In the arrangement shown'in Figure 1 the governing function is appliedto the radio frequency amplifier only. This is usually desirable forreasons already explained. The invention is not limited however to theregulation of a radio frequency amplifier, but may be applied in anydesired way to control the gain of the system or otherwise govern itsoutput.

Another mode of applying the governing function to an amplifier is shownin Figure 3. In

this case a separate regulator tube is not emthe governing E. M. F. isapplied directly to the grids of the amplifier tubes. The governorproper shown in this figure is similar to that shown in Figure 1, andthe corresponding parts are indicated by the same reference characters.In Figure 3 however the mode of applying the governing E. M. F. built upin the condensers C, C to control the gain of the amplifier isdifferent. The terminals of the governor condensers C, C are connectedrespectively to the cathodes and grids of the amplifier tubes RF-l andR.F-2, and the floating negative charge ployed, and

thus acquired by the grids becomes suflicientlygreat to choke off theanode current of these tubes, thus reducing the gain of the amplifier tothe required degree.

It will thus be seen that any slight increase in the output above thepredetermined limit will increase the governing E. M. F. and so reducethe gain of the amplifier that a further increase in the output isprevented. The output is thus fixed at a substantially constant value,irrespective of the input signal strength.

The type of radio frequency amplifier here shown is aperiodic and it isshown associated with a band selector of the type set forth in my UnitedStates Patent 1,725,433, August 20, 1929, but the invention may beapplied with equal elffeet to amplifiers of other types, includingselective or band amplifiers, for example those shown in my U. 8.Patents No. 1,666,518, April 17, 1928,

and No. 1,682,874, September 4, 1928.

Another means of regulating the gain of the system is shown in Figure 4.In this arrangement the governing E. M. I. set up in the governorelement C, G is used to regulate the output of a rectifier tube B whichsupplies the anode current of the amplifier, and so controls its gain.

' The rectifier tube B difiers from those ordinarily employed in havinga control electrode to which the governing E. M. F. is applied, thusincreasing the effective impedance of the rectifier and reducing theeffective anode voltage or current or both applied to the amplifier andcorrespondingly reducing its gain.

Various other modifications and applications of the invention willreadily suggest themselves, now

that the principle of the invention has been explained, and it will beunderstood that the invention is not limited to the particularembodiments shown and described, except as pointed out in theaccompanying claims.

I claim as my invention:

'1. The method of governing the output of an electrical amplifyingsystem for modulated signal waves which consists in amplifying anddemodulating the signal wave, deriving from the demodulated output afloating electromotive force whose value depends upon its maximumamplitude, employing this electromotive force to regulate the gain ofthe amplifying system, and slowly dissipating the floating electromotiveforce when the amplitude of the demodulated output decreases and therebyrestoring the gain of the amplifier.

2. The method of governing the output of an electrical amplifying systemfor modulated signal waves which consists in amplifying and demodulatingthe signal wave, deriving a floating electromotive force from thedemodulated output by rectifying the excess of the demodulated outputabove the floating electromotive force and emf ploying the floatingelectromotive force to regulate the gain of the amplifying system.

3'. The method of governing the output of an electrical amplifyingsystem which consists in deriving from the amplifying system analternating electromotive force proportionalto the output of the system,combining this alternating electromotive force with a directelectromotive force, deriving from the combination a governingelectromotive force depending on the excess of the alternatingelectromotive force over the direct electromotive force, and using thegoverning electromotive forceto regulate the gain of the amplifyingsystem.

4. The method of governing the output of an electrical amplifying systemwhich consistsin deriving from the amplifying system an alternatingelectromotive force proportional to the output of the system, combiningthis alternating electromotive force with a direct control electromotiveforce of controllable value, deriving from this combination a governingelectromotive force depending on the excess of the alternatingelectromotive force over the control electromotive force, using thegoverning electromotive force to regulate the gain of the amplifyingsystem and adjusting the control electromotive force and therebydetermining the output level of the system.

5. The method of governing the output of an electrical amplifying systemwhich consists in de riving from the system an alternating electromotiveforce proportional to the output, superimposing this alternatingelectromotive force on a direct electromotive force, deriving byrectification a floating charge depending on the excess of thealternating electromotive force over the direct 135 electromotive forceand utilizing this floating charge to regulate the gain of theamplifying system.

6. The combination with an electrical amplifier of means for derivingfrom the amplifier an 140 electromotive force dependent on the output ofthe amplifier, means for combining this electromotive force with adirect electromotive force, means for receiving the combinedelectromotive force, a condenser in which a floating charge is 145 thusexcited, and means whereby this floating charge regulates the gain ofthe amplifier.

'I. In an electrical amplifying system a radio frequency amplifier,means for converting the amplified radio frequency energy into audiofrequency energy, means for deriving from the audio regulating theoutput of the amplifier, and means governed by the output of theamplifier for automatically controlling the foresaid means.

9. In an electrical amplifier, a plurality of amplifier tubes, a sourceof power supplying the space current in these tubes, means located inthe circuit supplying the space current for regulating the output of theamplifier, and means governed by the output of the amplifier for,automatically controlling the aforesaid means.

10. In an electrical amplifier, a plurality of amplifier tubes, a sourceof power supplying the space current in these tubes, means forregulating the output of the amplifier comprising a regulator tubeinserted between the source of power and the amplifier, and meansgoverned by the output of the amplifier for automatically controllingthe effective impedance of the regulator tube.

11. In an electrical amplifier, a plurality of amplifier tubes, a sourceof power supplying the space current in these tubes, means forregulating the output of the amplifier comprising a regu lator tubeinserted between the source of power and the amplifier, a controlelectrode in the regulator tube, and means for impressing on the controlelectrode a governing electrcmotive force whose value depends upon theoutput or the amplifier thereby regulating the effective impedance ofthe regulator tube and automatically governing the gain of theamplifier.

12. An automatic governor for electrical amplifiers wherein are combinedmeans for deriving from the amplifier an alternating electromotiv'eforce whose value depends upon the output of the amplifier, a rectifierand a capacity connected in series relation, whereby the capacityacquires a floating charge by rectification of the alternatingelectromotive force, and means for utilizing the floating charge tocontrol the gain of the amplifier.

13. An automatic governor for electrical amplifiers wherein are combinedmeans for deriving from the amplifier an alternating electrornotiveforce whose value depends upon the output, a rectifier, a capacity meansfor impressing the alternating electromotive force on said rectifier andcapacity in series, whereby a floating electrometive force is set up byrectification, and a regulator element operated by such floatingelectromotive force whereby thegain oi the amplifier is regulated.

l i. An automatic governor for electrical amplifiers wherein arecombined meansior deriving from the amplifier an alternatingelectromotive force whose value depends on the output of the amplifier,a rectifier, a source of direct electromotive force, a capacityconnected in series relation with the two electromotive forces and therectifier whereby the capacity acquires a floating charge byrectification of the resultant electromotive force, and means forutilizing the floating charge to control the gain of the amplifier.

15. An automatic governor for electrical amplifiers wherein are combinedmeans for deriving from the amplifier an alternating electromotive forcedepending upon the output, means for superimposing this outputelectromotive force on a direct electromotive force, means forrectifying the excess of the output electromotive force over the directelectromotive force, a governor element in which a floatingelectromotive force is set up by such rectification, and a regulatorelement operated by such floating electromotive force whereby the gainof the amplifier is regulated.

16. An automatic governor for electrical amplifiers wherein are combinedmeans for deriving from the amplifier an alternating electromotive forcedepending upon the output, means for superimposing the outputelectromotive force on a direct electromotive force, means forrectiiyingthe excess of the output electromotive force over the directelectromotive force, a governor element in which a floating charge isset up by such rectification, a regulator element regulating the supplyof space current to the amplifier, and means for operating the regulatorelement by the floating electromotive force.

17. An automatic governor for electrical amplifiers wherein are combineda rectifier, a condenser, means for deriving from the amplifier analternating electromotive force whose value depends upon the output,means for impressing said electromotive force on the rectifier, meansfor exciting a floating charge in the condenser by rectification oi theexcess of said electromative iorceabove the floating charge, and meanscontrolled by the floating charge for regulating the gain of theamplifier.

18. An automatic governor for electrical amplifiers wherein are combineda rectifier, a condenser, means for deriving from the amplifier an 1oalternating electromotive force wnose value depends upon the output,means for impressing said electromotive force on the rectifier, meansfor exciting a floating charge in the condenser by rectification or" theexcess of said electromotive force above the floating charge, meanscontrolled by the fioating charge for regulating the gain of theamplifier, and means whereby the floating charge is slowly dissipatedwhen the output eleotromotive force decreases, thereby restoring thegain of the amplifier.

r annnarcrr is. vnnnrnnn.

@HQQLl- WMEFK l,926,l29.-Frcdcrick K. Vreclcml, Mcntclair, N.

Patent dated September 12, i933. Disclaimer ELECTRICAL AMPLIFIERS.

J. Govnarnne ran Unrrur or filed November 14, 1936, by the assignee,Vrceland Corporation. Hereby enters this disclaimer to claims 3, 4, 5,6, i2, i3, l4, l5, l7, and 18 in said patent.-

[Qfiiciai Gazette December 8, 1936.]

' CERTIFICATE OF CORRECTION.

Patent No. l,926.129. September 12. 1933.

FREDERICK K. VREELAND.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 4,line 143, claim 6, for ','rcceiving" read rectifying; and that the saidLettersPatent should be read with this correction therein that the samemay conform to the record of the case in the Patent Of-fice.

Signed and sealedthis 7th day of January, A. D. 1936.

Lee! ie Frazer .iiSeal) Acting Commissioner of Patents.

